1. Field of the Invention
The present invention relates to remediation of bodies of water, and, more particularly, to wetland technologies for such remediation.
2. Description of Related Art
Constructed and natural wetlands are commonly used for removing pollutants from wastewaters and surface waters. Within such “treatment” wetlands, many of the water-borne pollutants such as phosphorus and most metals are assimilated by biota or sequestered chemically. As the biota senesce and decompose over time, the sediments become the ultimate reservoir for these contaminants. It is important to note that natural wetlands typically accrete soils; so this gradual accumulation of sediments and associated constituents is a natural process. However, in wetlands that are intentionally used for removing contaminants from waters, the pollutant concentrations in the newly accreted sediments can exceed those of natural soil constituent levels, and the new sediments become somewhat enriched with pollutants. Additionally, depending on the type of aquatic vegetation (e.g., algae, floating plants, emergent plants) that occurs in the treatment wetland, the new sediments that accrete may exhibit physical characteristics (e.g., lower bulk density) that differ markedly from those of the native wetland soils.
Treatment wetlands frequently exhibit horizontal and vertical gradients in sediment pollutant concentrations and sediment accrual rates. The inflow region of the wetland, where concentrations of pollutants often are highest, typically exhibits greater sediment accumulation rates, and also higher concentrations of sediment pollutants than does the wetland outflow region. The gradual accumulation of sediments over time also results in vertical concentration gradients within the soil, with highest pollutant concentrations occurring in surficial sediments, and pollutant concentrations declining with sediment/soil depth.
One typical consequence of the accumulation of “contaminated” sediments within a wetland is a gradual impairment in treatment performance over time, since a flux of dissolved contaminants to the water column can occur from recently deposited, “enriched” sediments. Removal rates for some water-borne constituents, such as phosphorus (P), therefore may decline over time as the treatment wetland ages.
Several remedies have been proposed to rejuvenate treatment wetland sediments, and to restore the effectiveness of “old” treatment wetlands for removing water-borne pollutants. These techniques are comparable to those that have been utilized to rejuvenate lake and reservoir sediments. Addition of soil amendments, such as chemical coagulants, potentially can help stabilize and sequester sediment pollutants in water bodies. Bulk removal of accrued sediments also has been performed to reduce the volume of sediments, and mass of associated pollutants, from wetlands, lakes, and reservoirs.
While not commonly used for modifying water body sediments, fibrous organic matter amendments, such as wheat straw, have been applied to farm field soils to influence the mobility and bioavailability of constituents such as phosphorus.
Because treatment wetlands are a land-intensive treatment technology, the addition of amendments to immobilize soil pollutants, such as coagulants or organic matter, can be costly.
Therefore, it would be beneficial to provide a system and method for inexpensively amending soils and sediments.